Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $114.86   12.659%   $129.4001   $129.40   $129.40   $129.40  
  Purchase #2 $131.38   9.582%   $143.9688   $143.97   $143.95   $144.00  
  Purchase #3 $186.85   8.593%   $202.906   $202.91   $202.90   $202.90  
  Purchase #4 $46.86   8.323%   $50.7602   $50.76   $50.75   $50.80  
  Purchase #5 $179.54   5.111%   $188.7163   $188.72   $188.70   $188.70  
  Purchase #6 $207.29   13.108%   $234.4616   $234.46   $234.45   $234.50  
  Purchase #7 $72.84   10.149%   $80.2325   $80.23   $80.25   $80.20  
  7 purchase totals = $939.62       $1,030.4455   $1,030.45   $1,030.40   $1,030.50